Nano-porous metals refer to the metal materials having a porous structure composed of nano-size pores and adjacent metal ligaments. Nano-porous metal materials have the combined characteristics of nano materials, porous materials, and metal materials, have excellent physical, chemical and mechanical properties, such as nano-surface effect, high specific surface area, good electrical conductivity and thermal conductivity, etc., and have a wide application prospect in the fields of catalysis, separation, electron, optics, biomedicine and the like.
In recent years, due to the simple technique and high efficiency in preparation, the dealloying method has become an optimization method to prepare nano-porous metals. The method is a selective corrosion technology. The elements or alloy phases with relatively high chemical activity in the alloys are corroded under a chemical or electrochemical condition, and a nano-porous structure is formed by the remaining inert elements or corrosion-resistant alloy phases with relatively weak chemical activity through diffusion and/or self-organization. In accordance with the technique principle of the dealloying method, the composition and microstructure of the primary alloys (i.e. the precursors) suitable for preparing the nano-porous metal materials through the dealloying method must be uniform enough. In addition, a large electrode potential difference between the alloy elements, and fast enough diffusion velocity on the alloy/electrolytic solution interface for the inert elements should be considered. At present, most of the prepared nano-porous metals focus on the specific alloy systems containing noble metals and being capable of forming continuous solid solution single-phase alloy, for example, Au—Ag, Au—Zn, Au—Cu, Pt—Cu, Pd—Co, etc. Elements of these alloy systems are relatively monotonous in category, and limited in function characteristics.
Amorphous and/or amorphous+nanocrystalline alloys prepared by the melt-spinning technology have homogeneous composition and microstructure and various constituent element categories, and the size of the nanocrystalline grains can be controlled through the subsequent heat treatment. Therefore, amorphous/nanocrystalline alloys are suitable for preparing nano-porous metals as precursor materials. Moreover, in combination with the appropriate heat treatment and dealloying technique, not only alloy phases with different characteristics can be reserved or removed, but also the size of the formed nanopores can be controlled, so that nano-porous metal materials with specific function characteristics and controllable aperture can be prepared. Yu et al reported that nano-porous Pd can be successfully prepared using a Ni50Pd30P20 amorphous ribbon through dealloying [Yu et al, Chem Mater, 20(2010): 4548]. China invention patent CN102943187A disclosed a preparation method for preparing nano-porous Cu using Cu—Hf—Al noncrystalline. The applicant of this patent and the cooperator successfully prepared Au—Pd porous alloys with excellent catalytic activity and electrochemical stability by dealloying an Au30Si20Cu33Ag7Pd10 amorphous alloy [Lang et al, J Phys Chem C, 114(2010): 2600].
At present, the study on the nano-porous materials mainly focus on the fields of surface catalysis, biomedicine, sensing, filtration, surface enhanced Raman scattering, hydrogen storage and the like, but little study has been done on the magnetism of the nano-porous metals. Hakamada et al. prepared nano-porous Ni using electrochemical dealloying [Hakamada et al, Appl Phys Lett, 94(2009): 153105], but the coercivity is only about 100 Oe. There were few reports on the preparation of the nano-porous alloys with permanent magnetism using the dealloying method.
Ordered face-centered cubic L10-FePt phase shows excellent permanent magnetism due to the large uniaxial magnetocrystalline anisotropy, and has high saturation magnetization at room temperature. In combination with good wear- and corrosion-resistant and antioxidant characteristics of the Fe—Pt alloy, the Fe—Pt permanent-magnetic materials containing the L10-FePt phase can be applied to micro-electromechanical systems (MEMS), medical care, magnetic recording, and other fields. At present, most of the Fe—Pt alloys with permanent magnetism are in forms of bulk [Xiao et al, J Alloy Compd, 364(2004): 315; Gopalan et al, J Magn Magn Mater, 322(2010): 3423], film [Chen et al, J Magn Magn Mater, 239(2002: 471; Li et al, J Magn Magn Mater, 205(1999): 1] or nano particle [Takahashi et al, J Appl Phys, 95(2004): 2690; Sun et al, IEEE T Magn, 37(2001): 1239]. It is still a blank to prepare nano-porous Fe—Pt alloys with permanent magnetism. The applicant of this patent finds that the Fe—Pt—B amorphous or amorphous+ nanocrystalline alloy ribbons prepared by the melt-spinning technology may generate permanent magnets containing uniformly distributed nano-composite phases of ordered hard magnetic L10-FePt and soft magnetic Fe2B phases after appropriate heat treatment [Zhang et al, Appl Phys Lett, 85(2004): 4998; Zhang et al, J Alloy Compd, 615(2014): S252]. If the soft magnetic phases such as Fe2B in the alloys are removed using the appropriate dealloying technique subsequently, the nano-porous metal alloys containing single hard magnetic phase of L10-FePt are hopefully prepared, and the permanent magnetism thereof is further improved, thereby expanding the application range thereof.